LITTLE ROCK (AP) — Southwestern Electric Power Co. on Thursday began generating power at its $1.8 billion coal-fired plant in southwest Arkansas, a facility that spurred lawsuits from environmental groups until the sides settled after the company agreed to make concessions.

The plant has undergone weeks of testing, though SWEPCO gave no advance notice that the facility would start supplying electricity to the regional grid.

The plant joined the grid shortly after noon Thursday when a manager sent an email to Southwest Power Pool Inc., which manages the flow of electricity for the regional grid.

SWEPCO is planning a ceremony and open house at the 600-megawatt John W. Turk Jr. Power Plant in April, McCloud said.

Owners of a local hunting club along with the Sierra Club and Audubon Society sued to block completion of the plant. They also filed challenges with state regulators, but the sides came to an agreement late last year and construction went forward without further litigation.

Construction began in 2008 at the plant, which will supply enough electricity to light 450,000 homes.

Lev Guter, spokesman for the Sierra Club, said Thursday the group was disappointed the plant was able to open, but added that the fight was worth it because of the concessions to which SWEPCO agreed.

“Through our long battle we put an enormous amount of pressure against the coal industry. And through our alternative settlement on the Turk plant with SWEPCO, we got considerable concessions that will protect the public health and environment for all Arkansans,” Guter said.

SWEPCO agreed to shutter by the end of 2016 a coal-fired 528-megawatt plant near Pittsburg, Texas, and purchase 400 megawatts from renewable energy sources, most of which is wind power.

The utility also agreed to reimburse the environmental groups for $2 million in legal costs and contribute $10 million to other groups for energy-efficiency advocacy and land conservation efforts.

“Overall, that is a large step forward for Arkansas and that’s something we can certainly show at the end of our litigation,” Guter said.

McCloud said the company wasn’t concerned there would be protesters when the plant formally joined the grid and noted that the April 13 event has been publicly announced.

“We settled with all the opponents,” McCloud said.

SWEPCO, a unit of Columbus, Ohio-based American Electric Power, owns 73 percent of the plant. Other regional utilities in Arkansas, Oklahoma and Texas own minority shares.

The Turk plant sits on 3,000 acres between Fulton and McNab, Ark., and is using low-sulfur coal from the Powder River Basin in Wyoming.

SWEPCO, which serves 524,000 customers in Arkansas, Louisiana and Texas, says it is taking a balanced approach in fuel sources for its plants, using natural gas and coal.